Based on the Beijing Weather Modification Office Xband dual polarization radar’s observations of different types of rainfall in April to October 2009, the characteristics of raindrop size distribution of ZH-ZDR are given out, and can be expressed as a piecewise function, from which the hail parameters HDR are derived. If HDR>0, then there is hail, and if HDR<0, it means no hail. It is also pointed that the attenuation of electromagnetic waves can affect the results of HDR hail identification. By comparing the relations between HDR and the groundobservation hail data, the preliminary results have shown that the HDR above zero region is in good agreement with hail on the ground.